arm-trusted-firmware/plat/renesas/rcar/rcar_stack_protector.c

/*
 * Copyright (c) 2021-2023, Renesas Electronics Corporation. All rights reserved.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <stdint.h>

#include <arch_helpers.h>
#include <common/debug.h>

#define RANDOM_CANARY_VALUE ((u_register_t)0xDFF5FC8A720E205EULL)

u_register_t plat_get_stack_protector_canary(void)
{
	u_register_t cnt;
	u_register_t seed;
	u_register_t mul;
	u_register_t ret;
	uintptr_t val1 = (uintptr_t)__builtin_return_address(0U);
	uintptr_t val2 = (uintptr_t)__builtin_frame_address(0U);

	cnt = read_cntpct_el0();
	seed = (cnt ^ RANDOM_CANARY_VALUE) & ULONG_MAX;
	ret = seed;

	if ((ULONG_MAX/val1) > seed) {
		mul = (u_register_t)(val1 * seed);
		if ((mul < ULONG_MAX) &&
				((ULONG_MAX - (u_register_t)mul) > val2)) {
			ret = mul + val2;
		}
	}

	return ret;
}